Drier control



Aug. 17, 1965 T. R. sMrrH DRIER CONTROL Original Filed April 14, 1960 2 Sheets-Sheet 1 66 MMJM AGENT Aug. 17, 1965 T. R. SMITH DRIER CONTROL Original Filed April 14, 1960 2 Sheets-Sheet 2 Q Q W 22.

INVENTOR.

AGENT United States Patent 3,260,511 DRHER QONTRQL Thomas R. Smi h, Newton, iowa, assignor to The Maytag Company, Newton, Iowa, a corporation of Delaware Original application Apr. 14, 1960, Ser. No. 22,323.

Divided and this application Dec. 11, 1962, Ser.

2 Claims. {(1 34-45) This application is a division of Serial No. 22,323, filed April 14, 1960, now abandoned.

This invention relates to a control system in a machine for drying fabrics, and more particularly, to a system for automatically controlling termination of the drying operation after the fabrics have reached a predetermined degree of dryness.

Most of the conventional driers, especially of the home laundry type, regulate the drying period by a manually adjustable timer which is preset by the operator. The duration of the drying operation depends upon the judgment, or guess, of the operator as to the proper period for the desired degree of dryness. The results are inconsistent overdrying, underdrying, or, in the case of som fabrics, incomplete drying of particular pieces.

Heretofore, numerous control systems for domestic clothes driers have been attempted in an effort to obtain automatic termination of the drying operation in a domestic clothes drier after the fabrics have reached the desired dryness. One of the major problems facing any automatic control system is the difliculty in obtaining consistently completely dried loads of mixed fabrics as found in the home laundry, since different fabrics vary in their moisture retentivity. In addition, some fabrics have both light and heavy, thin and thick sections, to further complicate the problem.

One previous system has used the change in conductivity of the fabrics as the moisture is removed in order to discontinue operation of a drying machine at the moment electrical conductivity of the fabrics, as sensed directly between conductors in the drum, attains a predetermined value. This type of control causes premature shut-off of the machine before the clothes are completely dry, especially with mixed loads, which frequently occur in the home, because some of the pieces dry long before others and the wet pieces when enclosed in, or shielded by, drier pieces causes instantaneous premature shut-01f of the machine. In this type of control, since the drier operates only if a damp fabric is continuously contacting the electrodes, if at any moment none of the electrodes, or probes, within the drier drum contact a damp piece, the control will operate immediately to institute terminating of drying. For this reason the control is unreliable, and unsatisfactory.

In other control systems, the humidity of the air within the drier is measured to determine when the drying operation should be terminated, instead of direct measurements of the electrical conductivity of the fabrics. Humidity determinations are an unreliable index of the conditions of the fabrics, and control systems dependent thereon contain an inherent deficiency.

In still other systems attempts have been made to control the termination of the drying period by thermostats in the drier. In these systems the thermostats operate to shut-off the heaters when the temperature within the drying cabinet rises above a set value which occurs when most of the colthes have been dried. Again, the control does not insure that all of the fabrics have been dried.

It is an object of the present invention to provide a control system for a clothes drier responsive to the dry condition of the fabrics being treated. It is a further 3 ,Zhiifii i Patented Aug. 17, 1965 object of the invention to provide a system for controlling termination of a drying operation that is responsive to the isolated fabrics in a load, so as to obtain reliable shut-off of the drying operation. t is a still further object of the invention to provide a system whereby direct response of the control to the dryness or conductivity of fabrics is made practical or feasible for home laundry clothes driers. It is another object of the invention to provide a control system having a manually 0perable preselcction adjustment which initiates termination of the drying operation when the clothes have reached the manually preselected condition of dryness, for example, when the fabrics are in damp dry condition suitable for ironing. Further objects and advantages of this invention will become evident as the description proceeds and from an examination of the accompanying drawings which illustrate several embodiments of the invention and in which similar numerals refer to similar parts throughout the several views.

In the drawings:

FIGURE 1 is a view in vertical section, partly broken away, illustrating a drier which incorporates the control system of the invention;

FIGURE 2 is a bottom view of one of the baffles shown in the drum of the drier in FIGURE 1, illustrating the location of the electrodes;

FIGURE 3 is a schematic diagram of a preferred circuit employing the principles of the control system of the present invention.

Briefly described, the invention relates to a control system in which conductors, electrodes, or probes, directly contact fabrics being dried, and control termination of the drying operation after their electrical resistance, or

conductivity, dependent upon their condition of dryness,

exceeds a predetermined value.

In FIGURE 1 of the accompanying drawings is shown a clothes drier having a base frame iii which serves as a support for upstanding channel base members it and 12 which together with cross piece 14 support the hollow blower housing casting 17. Housing 17 includes a tubular portion 21, a divider wall 29 having a rearwardly flared inner portion defining an intake into an impeller chamber, and radially directed longitudinal webs 22 which converge toward each other to provide a retainer member 23. A passageway 26 is located between the tubular portion 21 and the bearing retainer member 23 which transverses the supporting webs 22.

Journalled within member 23 is a revoluble drum drive shaft 31 which projects from both ends of the housing 17. Amxed to drum drive shaft 31 at the rear of the cabinet is a large pulley 33 which is driven by motor 54 through motor pulley 36, main drive belt 3'7, a speed reduction system (not shown) and belt 40.

The opposite or forward end of the drum drive shaft 31 is rigidly connected to the drum spider member 46 which has radiating spokes 51 that support rim 52. A heat resistance sealing member 54 encircles the front pe riphery of blower housing 17 and the circular shoulder 55 located on the rear portion of drum spider 4-6.

A horizontally mount-ed tumbling drum dti has a rear wall 61 which is secured to rim 52 for support and rotation by shaft 321. Rear drum wall at is imperforate except for a central exhaust opening 62.

The periphery of rear wall 61 is flanged to form a supporting shoulder for the imperforate cylindrical side wall 65 which carries the clothes elevating vanes 66 for tumbling clothing within drum dti during rotation of the latter member. Cylindrical side wall 6S is connected to the front drum wall 67.

Front wall 67 has a centrally located access opening 68 and a circular perforate portion 69 located concentrically to access opening 68. This perforate portion 6%,

formed by several concentric rows of holes, serves as the air intake into drum 6%.

The cabinet 71) which is fastened to base frame 11) and which encloses the entire drying mechanism has an access opening 71 aligned to drum access opening 68 thereby allowing both of openings 68 and 71 to receive the door gasket 72. The door 73 is hinged and forms an airtight seal with gasket 72.

Fastened to cabinet 70 is the shroud or cowling member 74. Located between shroud '74 and the front drum wall 67 is an open coil electric heating element '75 which extends completely around the inside of cowling member 74 to raise the temperature of air passing through perforate portion 69 in the front drum wall 67. It will be understood that a gas heater may be used in place of the electrical element.

Air flow into drum 61 through the perforate area 69 and into the blower housing 17 is produced by rotation of the revoluble impeller member 76 located in blower housing 17. Fan pulley 77 is connected to the driving motor 34 by main drive belt 37. The blower housing casting 17 supports a cycling thermostat 73 which is connected in series with the heating element 75 in order to maintain the interior of drum 60 at the proper selected drying temperature. In practice, this switch is set to open at approximately 135.

Also connected in series with the heating element '75 is the high limit switch 79 which is mounted on an upper part of shroud member 74 so as to disconnect heating element 75 from its source of power in case the temperature near the front of the drum should rise above a predetermined selected temperature during the operation of the clothes drier, for instance, in the event of reduced air flow through drum 60.

In order to measure the electrical conductivity or resistance for determining the condition of dryness of the fabrics, electrodes or probes 30, 81 are mounted within the drum 60. In the form shown, the electrodes are spirally wound about each of the drum bafiles 66 to pro vide a maximum amount of contacting or probing surfaces exposed to the fabrics placed within the drum. As best illustrated in FIGURE 2, the electrodes are preferably set in recesses or grooves in the bafiles to prevent shorting therebetween by metatallic objects sometimes attached to the fabrics, for example, metal buttons, clips, buckles, and the like. It will be realized that different forms of electrodes, or probes, may be used, although the type disclosed herein is preferred.

Electrical energy is supplied to electrode 81 by lead 84 that is connected to brush 85 which engages the stationary slip ring 86 while the drum 61) is rotating. The slip ring 86 may be supported on an electrically insulative band 87 mounted on housing 17. Slip ring 86 is in turn connected to a lead 90 which runs to the control unit 92. Electrode 81 may also be supplied with electrical energy of the opposite polarity to electrode 80 by lead 83 that may be connected to a similar arrangement of brushes and slip rings. It is preferred, however, to ground electrode 81 to the rotatable drum 60, so that it is supplied by current from lead 91 which is also grounded to the framework of the drier.

The automatic control unit Q2 may be secured to the upper portion of the cabinet. Leads 919, 91 enter the control unit and are connected to the control circuit to be described hereinafter.

It will be noted that the bafiles 66 are formed of electrically non-conductive material in order to insulate the electrodes. However, the electrodes are electrically shorted by contacting the wet fabrics during tumbling. Ordinarily, a plurality of battles 66 are mounted Within the drum 6%, each of which is provided with electrodes 80, 81, and the respective electrodes of all the baffles connected in parallel.

Referring now to FIGURE 3 which illustrates the automatic control circuitry, there is shown diagrammatically d a timer means in the form of a timing cam stack 94 for controlling the drying operation. The cam stack has five cam switches 95 to 99 in which cam switch 95 controls the heater, cam switch 96 the timer motor, cam switch 97 the drive motor, cam switch 98 the sensing circuit, and cam switch 99 the damp dry setting.

It will be noted that the cam stack has regular dry and damp dry settings, either of which constitutes preselection means through manual operation of a knob (not SAOWD) by the operator. This preselection means includes damp dry setting in which resistor 131 is connected in parallel to resistor 113, as more fully explained hereinafter. It should be clear that the cam stack may include other selections, for example, for wash and wear fabrics, air fluff, and special loads.

The cam stack 94 is advanced by a timer motor mechanism 162 in three minute intervals, each of which three minute interval is represented by the vertical lines in the cam stack 94 in the drawing. The shaded areas in the drawing indicate that the circuit is completed, while the blank portions mean that the circuit is open at the time interval and for the cam switch specified.

The drier is energized by a conventional three wire system represented by power lines L L and N. The heater is connected between L and L for 220 volts A.C. by a circuit from L through cam switch 95, line 105, thermostat switch 78, high limit switch 79 to one side of the heater 75. The other side of the heater is connected to power line L through centrifugal switch 104 in motor 34. Centrifugal switch 104 is normally open. When motor 34- is rotated switch 104 is centrifugally closed to energize heater 75.

The timer motor 102 is energized by a circuit from power line L, on-otf switch 1100, cam switch 96, line 106 to one side of the timer motor 102. The other side of the timer motor is connected to power line N.

The drive motor is energized by a circuit from power line L on-otf switch 100, cam switch 97, line 107 to one side of the motor 34. The other side of the motor 34 is connected to power line N.

The sensing circuit is energized by a circuit from power line L on-olf switch 1%, cam switch 98, line 108.

The sensing circuit has a selenium half-wave rectifier 112 connected on one side to line 108 through line 111. The other side of the rectifier 112 is connected to capacitor 115 through a series resistor 113. The other side of the capacitor 115 is connected to power line N through series resistor 116. It will be noted that the electrodes 80, 81 within the drum are connected across the capacitor 115 by lines 99, 91. When the capacitor is charged by the DC. circuit from the rectifier 112, it may be discharged by any conducting material placed across, and shorting, the electrodes 31 81.

A gaseous discharge tube, such as a neon lamp is connected across capacitor 115. Neon lamp 120 normally has an infinite resistance; however, when the charge on the capacitor 115 reaches a predetermined value, the gas is ionized and the circuit is conducted therethrough to produce visible discharge.

A light sensitive cell 122 is positioned to detect the discharge of the neon lamp 120. One side of the light sensitive cell 122 is connected to line 108, and the other side of the light sensitive cell is connected to relay 125 through line 123. The other side of the relay 125 is fastened to power line N. Normally, when dark, the light sensitive cell 122 has a very high resistance. However, when it detects light, its resistance is greatly reduced and completes the circuit to energize relay 125.

Relay 125 operates switches 126 and 127. Switch 126 completes a holding circuit in order to maintain the relay 125 energized after the photo-electric cell 122 has been excited through the discharge of neon lamp 120. The holding circuit is from line 168 to line 128 through switch 126 to one side of the relay 125. The other side of the relay is connected to power line N.

Switch 127 controls the timer motor 102. When switch 127 is closed the timer motor is energized by a circuit from line 107, line 129, switch 127, line 130 to one side of timer motor 102. The other side of the timer motor N52 is connected to power line N.

It will be seen that the capacitor 115 is charged by a DC. circuit through the rectifier 112 and series resistances 113, 116 to power line N. The rate at which the capacitor 115 is charged depends, among other factors, upon the value of resistors 113, 116. It has been found that if the power between L and N is 110 volts 60 cycle alternating current, the capacitor 115 may be a 6 microfarads paper condenser and the total resistance of 113 and 116 is 31 megohms, or 30 and 1 megohms, respectively. The neon lamp in this arrangement may be designed to fire at 68 to 76 volts.

As the capacitor 115 is slowly charged through resistors 113, 116, it is also discharged through electrodes 80, 81 when the clothes are wet. However, as the clothes are dried, the average rate of discharge diminishes to a point at which the charge on the condenser reaches an amount which will fire the neon lamp 120. This operates the relay 125 through the photo-electric cell 122.

it will be apparent that resistors 113, 116 may be connected on the same side of capacitor 115. However, for safety reasons, it is better to divide the total resistance between the two sides of the capacitor.

From the foregoing, it is believed that the operation of the device is apparent. The operator opens the door 73 of the drier and inserts the fabrics in the drum 60. Next the cam timer 94 is manually set to regular dry position and the on-off switch ltlti closed. When the timer is set to the beginning of the regular dry position, the heater line 105 is connected to power line L through cam switch 95. Also, timer motor line 106, drive motor line 107 and sensing circuit line 108 are all connected to power line L, if the on-off switch 1% is closed through cam switches 96 to 98, as indicated by the shaded areas in the cam stack 94. The drive motor 34 rotates the drum 6th to tumble the clothes therein by baflies 66. After a certain rotational speed is achieved by the drive motor 34, switch MP4. is centrifugally operated to close the circuit to the heater '75.

The timer drive mechanism 182 when energized advances the cam stack 94 every three minutes. It will be noted that the timer drive mechanism 162 is maintained in energized position for a total of six minutes after which it is de-energized by the cam switch 96, as indicated by the blank area in the third three minute interval. When the timer drive mechanism is de-energized, continued operation of the drier is under control of the sensing circuit. The timer drive mechanism remains de-energized and the drier continues to operate until the timer drive mechanism is again energized to terminate the drying operation through actuation of the sensing circuit. With the timer drive mechanism tie-energized, the drier operation continues with the heater energized and the drive motor rotating to tumble the fabrics within the drum 60.

As long as the clothes remain wet, or sufficiently damp to effectively discharge the capacitor 115, the drying operation is maintained. Although the capacitor 115 is charged by the rectifier and through resistors 113, 116 it continues to be discharged by the fabrics shorting electrodes 8d, 81. However, when the moisture is removed, the fabrics achieve increased electrical resistance and the charge on the capacitor 115 begins to accumulate. The build up of the charge on capacitor 115 reaches a predetermined amount over a predetermined period of time of sufficient duration for all of the clothes within the drum to contact the electrodes during tumbling. Thus, if a damp fabric has been entrapped in dry fabrics, as the drum continues to rotate, the damp piece will eventually contact the electrodes 86, 81 and discharge the capacitor 115 to prevent termination of the drying operation. On the other hand, if the pieces are all dry, termination of the drying operation will be initiated.

Oneof the important features of the present invention is the time integration of the effective average resistance of the fabrics which fall across the probes with a predetermined average value necessary for initiating termination of the drying period. This reduces the occasion for premature termination of the drying operation.

After all of the fabrics have achieved a predetermined resistance for a predetermined period of time, the neon lamp 124? discharges. This excites light sensitive cell 122 to complete the circuit to the relay 125. When relay 125' is energized, it is maintained energized through the circuit completed through switch 126. The relay also completes a circuit through switch 127 to again energize the timer drive mechanism M52. The timer drive mechanism then begins to run through the remainder of the interval in the timer cam switch 96 and for two aditional three minute periods making a total of approximately six minutes. It should be noted that at the end of the first additional three minute interval the heater circuit is deenergized and at the end of the second three minute interval all remaining circuits are deenergized by the timer cam stack 94 and the drying operation discontinued.

The additional three minute heating period insures that the clothes will be completely dry, even in the folds or thick portions which are often found in fabrics of the home laundry. The last three minute period of operation without heat obtains a cooling period to bring the temperature of the clothes down to a comfortable handling temperature.

In the event the operator desires the clothes to be damp dry, a condition suitable for ironing, the timer cam stack 94 is manually positioned to damp dry. In this position operation of the device is similar to regular dry with two exceptions. The cam switch 99 connects resistor 131 in parallel to resistor 113. The circuit is completed by a line 132, cam switch 99, and line 199 to one side of resistor 131. The other side of resistor 131 is connected in parallel to resistor 113. Resistor 131 has, for example, a value of 330,000 ohms. This means that the total resistance in series with the capacitor is substantially reduced. Thus, the capacitor 115 is charged at a greater rate. The increased rate at which the capacitor 115 is charged results in the neon lamp 12d being fired at a time when the resistance through the clothes as sensed by the electrodes 80, 81 indicates the clothes are still damp. The charge on the capacitor 115 accumulates more rapidly through the reduced value of the total resistance and overtakes the discharge through the electrodes at an earlier fabric resistance, so that the clothes are partially damp when the neon tube is discharged.

As in the instance of the regular dry position, in the damp dry position the relay also completes a circuit through switch 127 to again energize the timer drive mechanism 1G2. he timer drive mechanism 1&2 then begins to run through the remainder of the interval in the timer cam switch 96 at which time all circuits are deenergized. In this way, the clothes in the damp dry position are subjected to less heat before the drive motor is stopped, so that they contain the desired amount of moisture.

In the drawings and specification there has been set forth a preferred embodiment of the invention, and although specific terms are employed, these are used in a generic and descriptive sense only, and not for purposes of limitation. Changes in form and the proportion of parts, as well as the substitution of equivalents are contemplated, as circumstances may suggest or render expendient, without departing from the spirit or scope of this invention as further defined in the following claims.

I claim:

1. In an apparatus for drying fabrics, a drum for containing fabrics, means for rotating said drum to tumble the fabrics, heating means for drying the fabrics in the drum, electrodes positioned for contacting and completing an electrical circuit through the tumbled fabrics,

sensing means responsive to the electrical resistance across said electrodes, timer means for controlling a series of operations for the drying of fabrics, said timer means including means for controlling the beginning of the drying operation including initiating rotation of the drum and energization of said heating means, said timer means including means for controlling the termination of the drying operation responsive to said sensing means, said timer means including means for sequentially advancing said timer means from said beginning to said termination of the drying operation, said timer means including means for stopping the sequential advancement of said timer means while controlling energization of said heating means andwhile maintaining rotation of said drum, and preselection means associated with said timer means for controlling said sensing means to respond selectively to a first predetermined preselected amount of higher electrical resistance across said electrodes to initiate termination of the drying operation by re-energizing said timer means and cutting oh said heating means after a first preselected quantum of heating or to respond selectively to a second predetermined preselected amount of lower electrical resistance across said electrodes to initiate termination of the drying operation by re-energizing said timer means and cutting off the heating means after a second different preselected quantum of heating.

2. In an apparatus for drying fabrics, a drum for containing fabrics, means for rotating said drum to tumble the fabrics, heating means for drying the fabrics in the drum, electrodes positioned for contacting and completing an electrical circuit through the tumbled fabrics, sensing means responsive to the electrical resistance across said electrodes, timer means for controlling a series of operations for the drying of fabrics, said timer means including means for controlling the beginning of the drying operation including initiating rotation of the drum and energization of said heating means, said timer means including means for controlling the termination of the drying operation by said sensing means, said timer means including means for sequentially advancing said timer means from said beginning to said termination of the drying operation, said timer means including means for stopping the sequential advancement of said timer means while maintaining rotation of said drum and energization of said heating means, and preselection means adapted for control by the operator and connected to said sensing means for controlling said sensing means to respond selectively to a first predetermined preselected amount of higher electrical resistance across said electrodes to initiate termination of the drying operation by said timer means and cutting off said heating means after a first quantum of heating or to respond selectively to a second predetermined preselected amount of lower electrical resistance across said electrodes to initiate termination of the drying operation and cutting off the heating means after a second different quantum of heating.

References Cited by the Examiner UNITED STATES PATENTS PERCY L. PATRICK, Primary Examiner.

NORMAN YUDKOFF, Examiner. 

1. IN AN APPARATUS FOR DRYING FABRICS, A DRUM FOR CONTAINING FABRICS, MEANS FOR ROTATING SAID DRUM TO TUMBLE . THE FABRICS, HEATING MEANS FOR DRYING THE FABRICS IN THE DRUM, ELECTRODES POSTIONED FOR CONTACTING AND COMPLETING AN ELECTRICAL CIRCUIT THROUGH THE TUMBLED FABRICS, SENSING MEANS RESPONSIVE TO THE ELECTRICAL RESISTANCE ACROSS SAID ELECTRODES, TIMER MEANS FOR CONTROLLING A SERIES OF OPERATIONS FOR THE DRYING OF FABRICS, SAID TIMER MEANS INCLUDING MEANS FOR CONTROLLING THE BEGINNING OF THE DRYING OPERATION INCLUDING INITIATING ROTATION OF THE DRUM AND ENERGIZATION OF SAID HEATING MEANS, SAID TIMER MEANS INCLUDING MEANS FOR CONTROLLING THE TERMINATION OF THE DRYING OPERATION REASPONSIVE TO SAID SENSING MEANS, SAID TIMER MEANS INCLUDING MEANS FOR SEQUENTIALLY ADVANCING SAID TIMER MEANS FROM SAID BEGINNING TO SAID TERMINATION OF THE DRYING OPERATION, SAID TIMER MEANS INCLUDING MEANS FOR STOPPING THE SEQUENTIAL ADVANCEMENT OF SAID TIMER MEANS WHILE CONTROLLING ENERGIZATION OF SAID HEATING MEANS AND WHILE MAINTAINING ROTATION OF SAID DRUM, AND PRESELECTION MEANS ASSOCIATED WITH SAID 